1. Field of the Invention
The present invention relates to a car power source apparatus and vehicle equipped with the power source apparatus, which is provided with battery-switches (e.g. relays or high power semiconductor switching devices) that connect the driving battery to the load, and a control circuit that controls the battery-switches.
2. Description of the Related Art
A car power source apparatus has battery-switches installed between the driving battery and the vehicle-side load (refer to Japanese Laid-Open Patent Publication 2005-269742).
The battery-switches are switched ON when the vehicle ignition switch (ignition key) is turned ON, and switched OFF when the ignition switch is turned OFF. Battery-switches in the ON state connect the driving battery to the vehicle-side load. The vehicle-side load includes a driving motor and generator connected via a direct current to alternating current (DC/AC) inverter. With the battery-switches in the ON state, the driving battery supplies power through the DC/AC inverter to the motor to drive the vehicle. Further, generator output charges the driving battery through the DC/AC inverter with the battery-switches in the ON state.
The battery-switches are controlled ON and OFF by a control circuit. The control circuit switches the battery-switches ON when it detects the ignition switch in the ON state, and switches the battery-switches OFF when it detects the ignition switch in the OFF state. In addition, the control circuit turns the battery-switches OFF when abnormal conditions are detected in the driving battery or vehicle. A control circuit that performs these functions is supplied with operating power from an auxiliary battery, which in almost all vehicles is a 12V lead-storage battery.
The auxiliary battery supplies power to various vehicle electrical components and accessories such as the power steering system and the (engine) starter motor. Consequently, when the power steering system or starter motor discharges high current from the auxiliary battery, the voltage of the auxiliary battery can drop temporarily. In particular, when the power steering system or starter motor discharges high current from an already degraded auxiliary battery, auxiliary battery voltage can drop markedly. The auxiliary battery is charged with power generated by an alternator, which is rotated by the engine, or by voltage stepped-down from driving battery output by a direct current to direct current (DC/DC) converter. However, since the charging current is limited to a constant specified current, extremely high load currents can cause the auxiliary battery voltage to drop. Further, when the auxiliary battery is in an uncharged state and the power steering system or starter motor pulls high current from the battery, its voltage will drop drastically. If auxiliary battery voltage drops drastically, control circuit operation can become unstable or the control circuit can become inoperable. When the control circuit fails to operate properly, the battery-switches cannot be controlled ON and OFF in the normal manner. In this situation, the battery-switches cannot be maintained in the ON state even though the ignition switch is turned ON, and power cannot be supplied normally from the driving battery to the motor.
The present invention was developed with the object of correcting the detrimental situation described above. Thus, it is an object of the present invention to provide a car power source apparatus and vehicle equipped with the power source apparatus, which is not affected by auxiliary battery voltage drop and can always maintain proper operation of the control circuit. It is another object of the present invention to provide a car power source apparatus and vehicle equipped with the power source apparatus, which does not require a dedicated power supply to keep the control circuit operating when power supply line voltage drops, but rather maintains control circuit operation with power from one segment of the driving battery. It is another object of the present invention to provide a car power source apparatus and vehicle equipped with the power source apparatus, which can set the voltage of power supplied to the control circuit to an optimum voltage and can supply operating power from the driving battery at the optimum control circuit voltage when power supply line voltage drops.